This invention relates to a valve assembly for brake fluid pressure control in an automotive vehicle and, more particularly, to a brake fluid pressure control valve assembly used in an anti-skid control apparatus.
As well-known in the art, an anti-skid control apparatus operates by sensing the premonitory symptoms of wheel lock-up when a brake is applied, interrupting hydraulic pressure by a cut-off valve, which is arranged between the brake master cylinder and wheel brake cylinder, upon detection of such symptoms, and increasing the volume of a hydraulic circuit on the wheel brake cylinder side to reduce the brake fluid pressure of the wheel brake cylinder, thereby causing a decline in wheel braking force. When the tendency of the wheels to lock has thus been mitigated, the apparatus decreases the volume of the hydraulic circuit on the wheel brake cylinder side to raise the brake fluid pressure, thereby increasing the wheel braking force.
In an anti-skid control apparatus of this kind, there is the danger that the cut-off valve will close accidentally due to a failure in the valve opening mechanism, as a result of which brake fluid pressure would be incapable of being supplied from the brake master cylinder to the wheel brake cylinder, thereby making braking impossible. An arrangement for alleviating this danger has been proposed in, for example, the specification of Japanese Patent Kokai-Publication No. 58-199258, in which a by-pass valve which opens in response to a failure in the cut-off valve opening mechanism is arranged in parallel with the cut-off valve.